Hurunui-Waiau Nutrient Budgeting Case Studies

Transcription

1 Hurunui-Waiau Nutrient Budgeting Case Studies Report Prepared by Rebecca Hyde & James Hoban This report outlines some considerations for the nutrient working group, relating to the Overseer nutrient budgeting exercise that Rebecca Hyde (Ballance Agri-Nutrients) has completed with four local farmers. Introduction This exercise has been carried out to look at nutrient loss on local dryland farms, under current management and several development scenarios. This has been done using Overseer for Nitrogen (N) loss while Phosphorus (P) has been handled subjectively through estimating the risk of P loss under each scenario. The ability of Overseer to provide accurate P loss estimates is discussed, with examples of how the use of a number of farm management practices will (or will not) effect Overseer outputs. When considering this project, the following points need to be kept in mind: 1 P is primarily lost to the environment through runoff. P binds to sediment and soil particles and is transported to streams in this way. Water flowing on farms in wet periods, which looks dirty, will have P in it. 2 The N loss being focused on is Nitrate leached through the soil. Rainfall, irrigation and free draining soils can all lead to higher leaching losses. A major driver of N leaching loss is urine, therefore the number of cows and heifers is an important influence (because of urine spots). Overseer is a model and as such will only ever provide estimates rather than infallible accuracy. Overseer assumes: 1 The use of annual average inputs and annual average outputs over a number of years 2 Near equilibrium conditions with minimal change each year 3 - Actual and reasonable inputs. Users need to understand how input changes alter outputs. Also assumed by Overseer is a level of good management practice. For each of the four case study farms: The Actual Nutrient Budget was completed for 2012/2013 Scenario 1 outlines a realistic development plan/real system 1 P age

2 Scenario 2 looks at the introduction of dairy grazing to the system All four case study farms are mostly medium soils with some blocks identified as stony. Overall there was no extreme variation in average nutrient loss figures as a consequence of variation in soil type. Soils have been identified using S-Map as per Overseer protocol. NIWA rainfall data has been used, as per Overseer protocol. How Topography is defined in Overseer This table has been included to as a reference for the group, given the time that has already been spent discussing the potential to limit nutrient loss by land class or slope. 2 P age

3 Farm 1 Sheep 84% & Beef 16% Lambs sold store Lucerne on river flats Sulphur Super applied to whole property Summer Rape grazed by sheep Cattle numbers variable Topography Percentage of Farm Flat 8.2% Rolling 0% Easy 33.4% Steep 52% Ineffective 6% Mean Annual Rainfall (MAR) 820mm N & P Loss/Risk N loss/kg/ha/yr % Increase N loss/ha P Risk Actual 8 Med Scenario 1 Improved Med Scenario 2 Dairy Grazing High Scenario 1 Changes made Scenario 2 Changes made Sheep 92% & Beef 8% Lucerne sown into grass Rape rotating through Easy hill grazed by sheep and cattle Ewe numbers and lambing % increased Finishing steers Hoggets mated N & S fertiliser added spring and autumn instead of P based fertiliser Sheep 72% & Beef 28% Increased Rape area N & S fertiliser added spring and autumn instead of P based fertiliser 300 Dairy Heifers Dec - May, 50 R2 steers finished Decrease ewe numbers, lambing % remains the same as actual Comments Majority of N leaching coming from Rape paddocks High Olsen P therefore potential for N & S options Property can get very wet during winter months Cattle percentage higher in Dairy scenario 3 P age

4 Farm 2 Sheep 65% & Beef 35% Lambs finished Summer Rape for sheep Breeding cows and trading cattle fertiliser applied MAR 800mm Topography Flat 5.4% Rolling 28% Easy 13.6% Steep 47.3% Ineffective 5% Percentage of Farm N & P Loss/Risk N loss/kg/ha/yr % Increase N loss/ha P Risk Actual 7 Low Scenario 1 Improved Low Scenario 2 Dairy Grazing Medium Scenario 1 - Changes made Sheep 75% & Beef 25% Increased rape Added Lucerne N - P - S fertiliser added Increased lambing percentage Mated hoggets Finished all lambs Improved pasture Scenario 2 - Changes made Sheep 75% & Beef 25% Kale added for winter grazing Added less Lucerne N, P S fertiliser added Increased lambing percentage Mated hoggets Finished all lambs Improved pasture 600 dairy cows wintered June/July 80 May-May heifers Breeding cows only beef stock, all claves sold store no trading cattle Comments Majority of extra N leaching coming from Kale paddocks 4 P age

5 Farm 3 Sheep 94% & Beef 6% Summer rape grazed by sheep Lambs finished Hoggets not mated Trading cattle Areas of the farm in brown top Lucerne Cut and Carried not grazed MAR 650mm Topography Percentage of Farm Flat 34.6% Rolling 56% Easy 0% Steep 2% Ineffective 7.4% N & P Loss/Risk N loss/kg/ha/yr % Increase N loss/ha P Risk Actual 8 Low Scenario 1 Improved Low Scenario 2 Dairy Grazing Medium Scenario 1 Changes made Sheep 93% & Beef 7% Lucerne increased - grazed and cut Rape stays the same Hoggets mated Phased N applied in spring across 80kg/ha Increased Ewe numbers by 200 All pasture ryegrass/white clover Scenario 2 Changes made Sheep 62% & Beef 38% 600 cows added June/July 300 heifers July/may Ewe numbers dropped hoggets All lambs sold store Lucerne Cut and Carried not grazed Kale added for winter grazing General Comments In dairy scenario more total N leached from kale block than from the whole farm in the actual scenario. 5 P age

6 Farm 4 Sheep 29% & Beef 71% Cattle - MA & young stock Fertiliser applied to flats only Pastures unimproved Hoggets not mated Lambs sold store Rape & turnips grown for autumn/winter feed MAR 1100mm Topography Flat 2% Rolling 9% Easy 15.5% Steep 27% Ineffective 45.6% Percentage of Farm N & P Loss/Risk N loss/kg/ha/yr % Increase N loss/ha P Risk Actual 3 Med Scenario 1 Improved 7 41 Med Scenario 2 Dairy Grazing 8 47 High Scenario 1 Changes made Sheep 64% & Beef 36% Cattle stayed the same Pasture improved on all areas of the farm Fertiliser applied to the flats and rolling with spring 30N applied to flats Turnip area increased All lambs finished Hoggets mated Ewe numbers increase Scenario 2 Changes made Sheep 65% & Beef 35% Dairy cows grazing kale on flats May-May heifers Pasture improved on all areas of the farm Fertiliser applied to the rolling country Turnip area increased All lambs finished Hoggets mated Ewe numbers increase Only breeding cows, all calves sold at weaning General Comments About half of total farm N is being leached from Winter fodder crops Kale & turnips 6 P age

7 Pros & Cons identified by the farmers for each development scenario: Scenario 1 Improved PROS CONS Sustainable way of farming Hit feed demand curve Have control over own stock Even out climatic risk Make the farm financially viable Provides opportunities for the next generation Enjoyment More work Lambing hoggets Scenario 2 Dairy Grazing: PROS Cash flow Diversification Infrastructure development CONS Issue with P runoff & N Leaching t sustainable Environmental impact within the farm gate pugging of soils Infrastructure development Ethics of some dairy farmers t having control of your own stock 7 P age

8 Phosphorus loss The P loss risk has been estimated for each scenario as being either low, medium or high. In making these assessments the following factors were considered: - Stock numbers - Stock classes - Winter grazing - Olsen P levels - Farmer s knowledge of the property i.e. erosion risk, wet winters etc - Soil type - Rainfall - Topography te - the estimate is based on inherent risk associated with the farming policy it is not a reflection of management. In reality, a high risk is still able to be managed well while a medium risk scenario, if managed poorly, could have a high environmental impact. There are significant opportunities to reduce or mitigate P loss risk though good farm management practices, many of which will not change Overseer P loss numbers. The following table shows a list of management tools that will result in less P loss to water, and explains whether or not their use is recognised by Overseer. Fencing Streams Phosphorus Loss Mitigation Appropriate fertiliser rates Conversion to more efficient irrigation system Avoiding high risk times for fertiliser application Change fertiliser type Targeting optimum Olsen P Precision fertiliser placement Cultivating with contour - rather than up and down slope Infrastructure to keep stock away from unfenced streams (e.g. troughs, shade) Culverts and bridges Managing track runoff Shifting break fences strategically Filter areas downstream of unfenced waterways Uncultivated ephemeral stream margins Erosion control plantings Spreading fertiliser evenly Reducing ability of stock to form camps Avoiding applying fertiliser directly into streams Rewarded in Overseer? Partially - already assumes very high efficiency Partially through lower application rates Partially - only if wetland able to be captured - assumed already 8 P age

9 In estimating P loss risk for each farm scenario, these tools have not been considered. Use of these tools would, in reality, mitigate increased P loss risk through many farm system changes and can be demonstrated though Farm Environment Plans. The ability of Overseer to handle these though is insufficient for realistically modelling improved management. Conclusions - The 10% rule is triggered by even the most conservative of improvements outlined in these case studies. - Developments considered in each scenario are not radical they are simply the type of changes many farmers have made before now. - It is not possible to foresee what future development options will be available to dryland farmers, so this exercise should be treated carefully and not as the basis for limiting future opportunities - Regardless of the scenario, N loss per ha from these dryland farms is relatively low, compared to intensive irrigated farming. - The range in N loss numbers from each farm, despite similar scenarios, is great enough that it makes limit setting by numbers challenging - P loss risk needs careful consideration with farm system changes but not through Overseer alone. Many P loss risks are able to be addressed through good farm management. 9 P age